User equipment (UE), also known as mobile stations, wireless terminals and/or mobile terminals are enabled to communicate wirelessly in a wireless communication system, sometimes also referred to as a cellular radio system. The communication may be made e.g. between two user equipment units, between a user equipment and a regular telephone and/or between a user equipment and a server via a Radio Access Network (RAN) and possibly one or more core networks.
The user equipment units may further be referred to as mobile telephones, cellular telephones, laptops with wireless capability. The user equipment units in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the radio access network, with another entity, such as another user equipment or a server.
The wireless communication system covers a geographical area which is divided into cell areas, with each cell area being served by a network node, or base station e.g. a Radio Base Station (RBS), which in some networks may be referred to as “eNB”, “eNodeB”, “NodeB” or “B node”, depending on the technology and terminology used. The network nodes may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the network node/base station at a base station site. One base station, situated on the base station site, may serve one or several cells. The network nodes communicate over the air interface operating on radio frequencies with the user equipment units within range of the respective network node.
In some radio access networks, several network nodes may be connected, e.g. by landlines or microwave, to a Radio Network Controller (RNC) e.g. in Universal Mobile Telecommunications System (UMTS). The RNC, also sometimes termed a Base Station Controller (BSC) e.g. in GSM, may supervise and coordinate various activities of the plural network nodes connected thereto. GSM is an abbreviation for Global System for Mobile Communications (originally: Groupe Spécial Mobile).
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), network nodes, or base stations, which may be referred to as eNodeBs or even eNBs, may be connected to a gateway e.g. a radio access gateway. The radio network controllers may be connected to one or more core networks.
UMTS is a third generation mobile communication system, which evolved from the GSM, and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UMTS Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using wideband code division multiple access for user equipment units. The 3GPP has undertaken to evolve further the UTRAN and GSM based radio access network technologies.
The 3GPP is responsible for the standardization of UMTS and LTE. LTE is a technology for realizing high-speed packet-based communication that may reach high data rates both in the downlink and in the uplink, and is thought of as a next generation mobile communication system relative UMTS.
In the present context, the expression downlink is used for the transmission path from the network node to the user equipment. The expression uplink is used for the transmission path in the opposite direction i.e. from the user equipment to the network node.
Currently, within the 3GPP, the potential benefits of uplink transmit diversity in the context of High-Speed Uplink Packet Access (HSUPA) is evaluated. With uplink transmit diversity, user equipment that are equipped with two or more transmit antennas are capable of utilizing some or all of them. In the initial phase of standardization of the Uplink Transmit Diversity (ULTD), only Open Loop Transmit Diversity (OLTD) is considered. In OLTD the user equipment autonomously decides the antenna weights. The user equipment selects the precoding vector with the assistance of the existing feedback from the network node, such as uplink Transmit Power Control (TPC) commands, Hybrid Automatic Repeat Request (HARQ) feedback, etc. In WCDMA the uplink TPC commands are sent on the downlink by the Node B via Dedicated Physical Control Channel (DPCCH) or Fractional Dedicated Physical Control Channel (F-DPCH) to control the uplink transmit power of the user equipment. The HARQ feedback information contains information such as ACK/NACK bits. The ACK/NACK is sent by Node B in response to the received data packet from the user equipment. In WCDMA the data packets are sent using Enhanced Uplink (EUL) mechanism via uplink data channel called as Enhanced Dedicated Channel (E-DCH). In WCDMA the ACK/NACK information is sent to the user equipment by the Node B via downlink control channel called as Enhanced HARQ Indication Channel (E-HICH). OLTD includes Open Loop Antenna Switching (OLAS) and Open Loop Beam Forming (OLBF). For WCDMA, the OLTD has been studied. The user equipment does the transmit adaptation of the at least two transmit antennas based on the available existing information. The OLTD according to the uplink TPC statistics is more of interest compared to other metrics such as HARQ feedback due to small delay, high frequency, and good availability.
The functionality of OLAS for WCDMA—High Speed Packet Access (HSPA) will now be explained. There may be at least two transmission antennas and at least one full-power power amplifier comprised in a user equipment capable of OLAS for HSPA. The user equipment may select the transmission antenna, among the at least two available transmission antennas, according to TPC statistics, e.g. following the algorithm:
Action A
Let TPC command DOWN be represented by −1 and TPC command UP by +1. Then let the user equipment accumulate all received TPC commands.
Action B
At each frame border the accumulated TPC sum is compared with 0. If the sum is larger than 0 the transmit antenna is switched.
Action C
If the same transmit antenna has been used for x consecutive frames the user equipment automatically switches antenna. x may be referred as the forced switch circle and determined according to the radio environments.
Action D
Every time an antenna switch occurs the accumulated TPC sum is reset to 0.
When performing OLBF, the situation is somewhat different. The user equipment comprises at least two transmit antennas and e.g. two power amplifiers in the user equipment capable of OLBF for HSPA. With e.g. the herein described algorithm, the user equipment may adjust the beam by adjusting the phase bias between two transmit antennas based on the received TPCs:
1. The phase offset, δ, may be set to e.g. 48 degrees, while ε may be set to e.g. 12 degrees.
2. Let TPC command DOWN be represented by −1 and TPC command UP by +1.                a. Initial relative phase between two transmitters Δφ=−δ/2 for the first slot (#1 slot). ε may be set to zero until two TPC commands become available to the user equipment.        b. Apply relative phase for the next slot Δφ=Δφ+δ        c. Determine new relative phase:                    1. if TPC1>TPC2, Δφ=Δφ+ε            2. if TPC2>TPC1, Δφ=Δφ−ε            3. otherwise, no change            Note that TPC1 and TPC2 correspond to slot (1,2), (3,4), . . . , (i*2−1, i*2), where i=1 to n.                        d. Apply relative phase for the next slot Δφ=Δφ−δ        e. Go to step b.The measurement of propagation delay (PD) within a network may be calculated:PD=(RTT−UERx-Tx)/2  Equation 1Where PD is the propagation delay; UERx-Tx is the time difference between receiving and transmitting at the user equipment while RTT is the Round Trip Time, which is measured by the UTRAN (i.e. by the network node/Node B). Thus the UERx-Tx may be defined as the difference in time between the user equipment uplink Dedicated Physical Control Channel (DPCCH) frame transmission and the first detected path (in time), of the downlink Dedicated Physical Channel (DPCH) or Fractional-DPCH (F-DPCH) frame from the measured radio link. There are two defined methods to measure the UERx-Tx time difference: Type 1 and Type 2.        
For Type 1, the reference reception path may be the first detected path (in time) amongst the paths (from the measured radio link) used in the demodulation process.
For Type 2, the reference reception path may be the first detected path (in time) amongst all paths (from the measured radio link) detected by the user equipment. The reference path used for the measurement may therefore be different for Type 1 and Type 2. The reference point for the UERx-Tx time difference may be the antenna connector of the user equipment. Measurement may be made for each cell included in the active set.
The Round Trip Time (RTT) may be defined as:RTT=TRX−TTX  Equation 2where TTX is the time of transmission of the beginning of a downlink DPCH or F-DPCH frame to the user equipment and the reference point for TTX may be the transmission antenna connector; TRX is the time of reception of the beginning (the first detected path, in time) of the corresponding uplink DPCCH frame from the user equipment and the reference point for TRX may be the reception antenna connector.
In addition the Physical Random Access Channel (PRACH) propagation delay which is measured by the network node/Node B may also be specified as a separate measurement in WCDMA/HSPA. The measurement enables the network node/Node B to measure one way propagation delay between the user equipment and the network node/Node B during the PRACH transmission by the user equipment.
The TPC delay comprises the signal processing delay in the network node, D-NB, the propagation delay in the air interface D-P and the signal processing delay in the user equipment, D-UE:
D-NB may be defined as the time between the start of receiving the uplink DPCCH slot and the time the uplink TPC is generated and prepared for downlink transmission. D-NB is thus known to the network node.
D-P is the propagation delay which depends on the distance from the user equipment to the network node. D-P may be estimated by the network node by applying Equation 1 and/or Equation 2.
D-UE may be defined as the time between the start of the receiving of the downlink slot which carries the uplink TPC and the time the uplink TPC is decoded. D-UE is known to the user equipment.TPC delay=D-NB+D-P+D-UE  Equation 3The TPC delay may comprise 2 to several slots depending on the mentioned delay components above. For instance, the TPC delay may increase several slots dependent on the type of uplink receivers.
Concerning the previously discussed OLAS scheme, the user equipment selects antenna based on the received uplink TPC commands in the period when the antenna is used. FIG. 1A shows the timing relationship between the time when the antenna is being used and the time when the generated TPCs based on the uplink DPCCH quality during this period is received at the user equipment. The decision to continue using antenna 1 is taken based on the TPC command received in period T1 and the decision to continue using antenna 2 is taken based on the TPC command received in period T2. As seen when studying FIG. 1A, the decision made based on the TPC command received in the periods T1 and T2 respectively, due to the TPC time delay, may be erroneous, as the decision may be based on transmissions in fact made by the other antenna.
FIG. 1B illustrates the corresponding situation of interaction between TPC delay and OLBF. By comparing the received TPC commands corresponding to the two opposite beam directions, the user equipment determines which direction is correct for beam adjustment and the uplink precoding vector is determined accordingly. FIG. 1B shows the timing of TPC commands for channel sounding. However, a mismatch due to the TPC delay may be critical for finding the correct beam direction.
The problem e.g. in the scenarios discussed in conjunction with OLAS in FIG. 1A and/or OLBF in FIG. 1B is that the user equipment does not know the TPC delay. This may degrade the performance of OLTD and the system performance in uplink.
For OLAS, the ignorance of TPC delay may have following consequence. All the uplink TPC commands received by the user equipment during its time window of statistics may not be generated by the network node, based on the uplink DPCCH quality when the same transmit antenna is used by the user equipment. This decreases the reliability of selecting the antenna based on the uplink TPC statistics. This means the probability to select the poor antenna is increased.
For OLBF, the ignorance of TPC delay may result in that the user equipment may compare the wrong TPC commands during channel sounding phase. This means that the uplink beam may be generated in the wrong directions and consequently the uplink performance of the user equipment is seriously degraded. This also degrades the uplink received signal quality at the network nodes/base stations which receive the misdirected beam.
The high error probability of antenna selection for OLAS or precoding vector selection for OLBF degrades the perceived uplink quality for the user equipment, which in turn also increases uplink power consumption of the user equipment. Furthermore this also causes large variation of the uplink load/interference/Rise-over-Thermal (RoT) in the system and even overall increase in the uplink load/interference/RoT.